1. Field of the Invention
The present invention relates to a thermoplastic sheet having an electroconductive surface.
More particularly, the present invention relates to a nap-free thermoplastic electroconductive sheet of an electroconductive fiber.
2. Description of the Prior Art
Heretofore, as methods for rendering plastics electroconductive, there is a method for blending an antistatic agent with plastics or applying it on the surface of the plastics, and a method for blending carbon black as an electroconductive material with plastics. However, in the former method, an obtained sheet is only improved to a surface resistance of not more than 10.sup.11 .OMEGA. or so, and it has the drawback that the surface resistance varies with circumferential humidity.
In the latter method mentioned above, a desired conductivity cannot be obtained if carbon black particles are not blended in such a large amount as to be continuously present in the sheet. However, the use of much carbon black noticeably deteriorates mechanical strength of the basic resin. Furthermore, since the tint of the product is black, colors other than black cannot be obtained. As a technique by which the conventional problems described above are solved, a method has been disclosed in Japanese Patent Publication Laid-Open No. 58-155917 which comprises laminating, by melt extrusion, a basic thermoplastic resin to a nonwoven fabric (electroconductive nonwoven fabric) prepared by irregularly twining an electroconductive fiber into a hot-melt adhesive fiber, and pressing the resulting laminate integrally.
However, in the electroconductive sheet obtained by this method, the electroconductive fiber is present on the surface thereof, and therefore when the sheet is rubbed, the electroconductive fiber is napped and the appearance of the sheet degrades. Moreover, strands of the electroconductive fiber fall off therefrom, and the electroconductive fiber further contaminates surroundings disadvantageously.